1. Field of the Invention
The present invention relates to noise silencers, and more particularly to reactive silencers comprising one or more expansion chambers with extended inlets and outlets for use with internal combustion engines.
2. History of the Prior Art
It is known to attenuate noise from sources such as internal combustion engines using reactive silencers comprised of one or more expansion chambers with extended inlets and outlets. Such silencers operate on the principle that an impedance mismatch causes sound energy to be reflected back toward the source instead of being radiated. Examples of silencers of this type are shown in U.S. Pat. Nos. 3,741,336, 2,765,044 and 3,807,527, and in an article by E. J. Wonnacott at pp. 17-26 of the Journal of Sound and Vibration (1974) 37(1) entitled LOWER EXHAUST NOISE FROM BETTER SILENCER DESIGN TECHNIQUES.
The problem with many prior art silencers of this type lies in design difficulties. Designing a silencer for a particular application is usually a haphazard process at best, and often results in configurations of considerable complexity and expense. Due to a lack of understanding of the apparatus involved, many silencers have been assembled on a trial and error basis with various components being added or substituted until the attenuation appears to be acceptable. At that, it is often found that the attenuation will vary significantly over even a limited range of frequencies so as to detract from the versatility of the silencer. For example, the Wonnacott article which shows a pair of expansion chambers and connected tailpipe fails to recognize that the tailpipe acts to attenuate sound at specific wavelengths similar to extended inlet and outlet tubes. This affects the design configuration of the silencer and recognition of this permits a better design for attenuation over a wide frequency range.
Accordingly, it would be desirable to provide a noise silencer which is of relatively simple and economical design and yet which provides substantial attenuation of unwanted noise over a relatively broad frequency range.
It would furthermore be desirable to provide a noise silencer which is easily designed for a specified application using a systematic approach.